1. Field of the Invention
This invention relates to a device for purifying exhaust gas from an internal combustion engine, said exhaust gas being one of atmospheric pollution sources, and more particularly to a catalyst converter for purifying the exhaust gas by using catalysts.
The mixture gas of air with fuel to be fed in cylinders of an internal combustion engine is subjected to combustion and explosion within said cylinders, followed by discharging as an exhaust gas outside the cylinders. Such an exhaust gas contains incomplete-combustion gases such as unburned hydrocarbons, carbon monoxide and the like and toxic gases such as NOx produced due to combustion at an elevated temperature.
By the term "a catalyst converter" as used herein is meant a converter which uses catalysts for treatment of an exhaust gas, said treatment comprising the steps of oxidation, reduction, filtration or adsorption of toxic gases contained in exhaust gas, followed by discharge of exhaust gas into atmosphere.
2. Description of the Prior Art
One of the conventional type catalyst converters of the prior art is provided with a member which supports a catalyst holder disposed substantially in the center of a casing having inlet and outlet pipes, with its opposite side portions of said holder being in engagement with the inner walls of said casing, and which defines within the casing a passage for exhaust gas. Another of the conventional type catalyst converters is provided with a member which is located within the casing in concentric relation therewith as in the preceding case and which contains honeycomb catalysts therein and defines a passage for exhaust gas. Such a catalyst converter is so designed as to maintain constant the flow passage of exhaust gas within the catalyst converter and not to extremely lower the output of an engine during the normal operation thereof, thereby achieving efficient purifying action of exhaust gas.
In general, as reported on LA No. 4 mode test, the adverse or toxic components of the exhaust gas discharged during operational conditions covering from the starting, warming-up and the subsequent phases of run of an internal combustion engine are particularly contained in a great amount in the exhaust gas which is discharged for a period from the starting of an engine to the completion of warming-up period.
On the other hand, since the catalysts contained in catalyst converters used with internal combustion engine for purifying said exhaust gas are heated to an activating temperature, principally by means of exhaust gas passing through the catalysts from the internal combustion engine, the temperature of catalysts after the warming-up operation of the engine will reach almost the activating temperature of the catalysts. For this reason, even if a conventional type catalysts converter is provided for the internal combustion engine, the temperature of the catalysts contained in the catalyst converter is maintained below their activating temperature, i.e. before the warming-up run of the internal combustion engine, the converter will fail to achieve sufficient purifying effect on toxic gases, such that the internal combustion engine discharges a great amount of toxic gases into the atmosphere. Accordingly, in order to enhance the purifying action of a catalyst converter before the warming-up run of the internal combustion engine, it is necessary to rapidly raise the temperature of catalysts.
To this end, an attempt may be proposed, in which the cross sectional area of the catalysts layer passing exhaust gas therethrough is reduced so as to minimize the radiation of heat therefrom for the purpose of imparting the heat contained in the exhaust gas to catalysts, thereby accelerating the rate of the temperature rise of the catalysts. However, there will arise a problem that the pressure of the exhaust gas is increased due to such a high level of the load application, with accompanied excessive loss in power output of an engine.